As a technology for improving cell throughput in a 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) downlink, there is frequency scheduling (multi-user scheduling). Each terminal feeds back to the base station a CQI (Channel Quality Indicator) that is determined based on an SINR (Signal to Interference and Noise Ratio) for each group of a plurality of subcarriers (hereinafter “RB (Resource Block),” and the base station allocates communication resources to terminals using these CQI's.
The base station allocates a communication resource preferentially to a terminal that feeds back a higher CQI. Consequently, since the number of terminals that feed back a high CQI increases as the number of terminals increases, there is an improvement in cell throughput (peak data rate and frequency utilization efficiency), CQI feedback methods include Best-M reporting.
FIG. 1 shows an overview of Best-M reporting. In Best-M reporting, an average CQI (represented by X bits) of an entire transmission band (NRB), CQI's corresponding to the top M RB's with a high CQI level (the CQI of each RB being represented by Y bits) and the positions of selected RB's (represented by log2(NRBCM) bits) are fed back. By this means, a total of X+YM+log2(NRBCM)) bits are fed back. Number of quantization bits Y of the top M CQI's is represented by a difference value from the average CQI. Also, the average CQI is represented by fixed number of quantization bits X, regardless of the transmission band.
FIG. 2 shows the CQI feedback format in Best-M reporting. Here, a case is shown in which X=5 bits, =3 bits, and M=5. The base station demodulates Best-M reporting feedback information, and reproduces the CQI of each RB.